Anchorage for concrete stressing tendons



Dec. 27, 1966 E. K. RICE 3,293,811

ANCHORAGE FOR CONCRETE STRESSIG TENDONS INVENTOR 50M/A RD K /Q/CE BY MKMI TTO/QA/EMS Dec. 27, 1966 E. K. RICE ANCHORAGE FOR CONCRET E STHESSINGTENDONS 5 Sheets-Sheet 2 Filed June 1, 1965 INVENTOR., K /Q/CE TTO/QA/EV5 EDM/A120 BY Dec. 27, 1966 E. K. RICE 3,293,811

ANCHORAGE FOR CONCRETE STRESSING TENDONS Filed June 1, 1965 3Sheets-Sheet 5 INVENTOR,

BY MA TTO/Q/VEi.;

United States Patent O 3,293,811 ANCHORAGE FOR CONCRETE STRESSINGTENDONS Edward K. Rice, 2077 Linda Flora, Los Angeles, Calif. 90024Filed June 1, 1965, Ser. No. 460,234 9 Claims. (Cl. 52-223) Thisinvention relates to anchorages for concrete stressing tendons, moreparticularly to d evices for use in the tensioning of concrete beamtendons after the concrete has set, and is a continuation-in-part of mycopending applications for Anchor Means for Concrete PrestressingTendons, Serial No. 821,876, filed June 22, 1959, now abandoned; andAnchorage for Concrete Stressing Tendons, Serial No. 159,214, yfiledDecember 14, 1961, now abandoned.

Included in the objects of this invention are:

First, to provide an anchorage for concrete stressing tendons of thetype which are cast in place in such a manner that they may be tensionedafter the concrete has been set, the anchorage including a wedge andtendonreceiving conical bore, and an external, radially extending,constraining plate dipped in a plane passing through the midportion ofthe tendon wedges placed in the conical bore so that the radial forcesproduced by the interaction of the tendons and their wedges is nottransmitted to the surrounding concrete; the c-onstraining plate alsoserving to distribute the axial load of the tendon over a large area ofthe concrete.

Second, to provide an anchorage for concrete stressing tendons in whichan embodiment thereof utilizes a singlepiece wedge-receiving member andconstraining plate.

Third, to provide an anchorage for concrete stressing tendons in whichan embodiment thereof utilizes a wire coil as the wedge-receivingmember.

Fourth, to provide an anchorage for concrete stressing tendons whereinan embodiment thereof utilizes la cylindrical member continuing axiallyfrom the wedge-receiving member, the cylindrical member having means fortransmitting and distributing to the surrounding concrete the axialloads imposed by the tendon.

Fifth, to provide an anchorage of this type which in cludes further arubber or elastomeric plug initially received in the wire coil, and heldin bearing engagement with the concrete form when the anchorage issecured tothe form, so as to provide a wedge and grout-receiving cavity,the plug forming an effective seal means to exclude concrete from .thewedge-receiving member while the concrete is being poured.

Sixth, to provide an anchorage which utilizes a temporary sleevesurrounding the tendon and extending beyond the tendon to the wrappingor jacket which covers the major length of the tendon, so as to form,when the sleeve is withdrawn, an annular space between the tendon andanchorage into which a dense grout or other sealing and bonding age-ntmay be forced.

Seventh, to provide an anchorage of this type which incorporates meansfor venting air and liquids during the grouting operation, thereby toensure complete filling of any voids.

Eighth, to provide an anchorage for concrete stressing tendons utilizingserrated gripper elements wherein the steel tendon is coated in theregion of the gripper elements of the anchor means with a bondedcoating, thereby to minimize stress concentration at the points ofcontact of the gripper serrations.

Ninth, to provide an anchorage for concrete stressing tendons which maybe arranged to permit bonded encasement of a selected length of thetendon inwardly of the gripping elements to improve the fatigueresist-ance of the anchorage.

3,2 93 ,81 l Patented Dec. 27, 1966 ice With the above and other objectsin view as may appear hereinafter, reference is directed to theaccompanying drawings in which:

FIGURE l is a fragmentary, sectional view showing lan end of a concretebeam and tendon and la portion of an end form, and showing anchorage inplace before api plication of tension to the tendon;

FIGURE 2 is a similar fragmentary, sectional view, showing an end of thecompleted beam after the tendon has been subjected to tension and sealedin place;

FIGURE 3 is a transverse sectional View taken through 3-3 of FIGURE 1,showing particularly the hoop stress-resisting plate;

FIGUURE 4 is a diagrammatical plan view show-ing the manner in whichstressing tendons may be arranged in a concrete beam or slab;

FIGURE 5 is a fragmentary, sectional view similar to FIGURE l, showing amodified construction which includes means for forming a grout-receivingcavity between the tendon and anchorage and for venting air and liquidtherefrom;

FIGURE 6 is a similar fragmentary, sectional view showing an end of thecompleted beam after the ytendon has Ibeen subjected to tension and thegrout-receiving space has been filled with grout;

FIGURE 7 is a fragmentary, sectional view showing an end of a concretebeam tendon and a portion of an end form, and illustrating a furthermodified form of the anchorage;

FIGURE 8 is a similar fragmentary, sectional view showing an end of thecompleted beam;

FIGURES 9 through 13 illustrate a further modified form of the anchorageparticularly adapted for tendons of larger size, in which:

FIGURE 9 is an inner end view of the wedge-receiving member andconstraining plate;

FIGURE 10 is an outer end view thereof;

FIGURE ll is a longitudinal sectional view thereof showing a `sealingplug in place and indicating a tendon and portion of a formfragmentarily;

FIGURE 12 is a longitudinal sectionalview similar to FIGURE ll showinganchorage after tensioning of the tendon; and

FIGURE 13 is a transverse sectional view taken through 13--13 of FIGUREl2 with the surrounding concrete omitted.

Prestressed concrete beams or slabs 1 are cast within suitable forms 2,an end of which is indicated fragmentarily. Within the beam is one ormore stressing tendons 3 which extend lengthwise of the beam 1 andprotrude from the ends thereof. Each tendon may be a single wire or amultiple Wirestrand, or a more complex cable of essentially circularcross-section, If theV concrete beam or slab 1 is stressed by apost-tensioning process, the tendons are placed in the form beforepouring the concrete and are initially substantially tension free. Thetendons are covered by a sleeve or wrapping 4 having a sufficiently lowcoefficient of friction to permit elongation of the tendons 3 after theconcrete has set.

The concrete beam or slab 1 thus far described and the post-tensioningtechnique are conventional. In the exercise of the present invention, aspecial anchorage is provided at one or both ends of each tendon 3.

With reference first to FIGURES 1 through 4, each anchorage includes ahelically coiled wire structure 5 which in turn, includes a cylindricalsleeve member 6 surrounding the tendon 3 commencing at a predetermineddepth from the end of the tbeaim. The inner end of the sleeve member 6may be covered by an extremity of the sleeve or wrapping 4.

The outer end of the sleeve member 6 merges into or is formed to aconical wedge-receiving member 7, The conical mernber 7 divergesoutwardly towards the end of the beam 1. The conical member 7 forrns aninternal conical socket adapted to receive gripping wedges 8, which arecomplementary, to form a cone, the outer surface of which has a slopeconforming to the slope of the conical socket. Internally, the wedges 8have teeth 8a.

The conical member 7 of the coi-led wire anchorage structure isencircled by a hoop stress-resisting plate 9 v foaming a radially rigidconstraining means which may be in the form of a square with a circularhole, the walls of which are adapted to engage the conical portionrnidway between its ends. The hoop stress-resisting plate 9 is cementedby a high -strength adhesive, such as an epoxy resin, or is secured bybrazing as indicated :by 9a, or otherwise secured in place so as toremain fixed and resist axial loads, particularly in a direction towardthe larger end of the conical member. The four corners of the plate 9are apertured to receive nails 10` which are adapted to be driven intothe form 2.

The anchorage structure 5 receives a segmental plug 11, which servesboth as a seal and a mounting means. The plug is formed of rubber orother elastomer, and is split longitudinally, preferably in twocomplementary halves. The plug 11 includes Aa conical portion 12 whichlits within the conical member 7 of the anchorage, and an enlargedcylindrical portion 13 which is interposed between the anchoragestructure 5 and the yform 2. The nails may be driven into the formaround' the plug 11 or the plug may be longitudinally perforated toreceive the nails. The fonm is, of course, apertured so that the tendonmay extend therethrough.

The plate 9 provides a convenient means for locating reinforcing bars 14extending transversely to the tendon 3.

If the anchorage is used in the casting of concrete slabs, the tendons 3may be arranged in pairs and diverge at their ends, as indicated by 15,into separate anchorages.

The anchorage is utilized as follows: y

Prior to the pouring of a concrete beam or slab 1, the ends of a seriesof tendons 3 are extended through the anchorages and through the ends ofthe form 2. The individual anchorages are secured in place by nailsdriven through the plates 9. Sui-table reinforcing bars 14 and otherreinforcing bars are added, and the concrete is poured. After theconcrete has set and developed the prerequisite strength, the form isremoved, the segmental plugs 11 are extracted, and the gripping wedges 8are inserted.

The tendons 3 are then placed under tension `by use of .conventionaljacks and are held in tension by the gripping wedges 8. The tendons 3are then cut so that their outer ends are within the cavities formed by-the plugs 11, and these cavities are lled with grout. The wedges 8 formslots therebetween so that the 4grout 16 may pass between the wedges 8and into the space between the sleeve portion 6 of the anchorage member5 and the tendons 3, if this space has not previously been -lled withthe concrete. It should tbe noted that concrete may seep through thecoils of the anchorage member 5 in the region beyond the Isegmentalplugs 11.

It should be noted that the plate 9 defines a plane passy the wedges.

In an absolute sense, through, the inner or smaller end of the wedgesmay undergo a slight radial expansion,

lbut not enough to lose their gripping action, In fact, such slightexpansion as may occur minimizes stress concentration.

The tendon ,is formed of hardened steel; however, the wedges are heattreated sonas to Vbe harder than the tendon. The teeth 8a are not sosharp as to nick the tendon |but to impress therein.

Reference is now directed to FIGURES 5 and 6. The construction hereillustrated incorporates a renernent which insures a space between thetendon 3 and the anchorage structure S which -may later be tiled withgrout.

Added to the structure shown in FIGURES l through 4 is a tubular endlitting 17 which is suitably secured to the extended end of the sleeveportion 6. Attached to the end tting 17 is a vent tube 18 which curvesinto parallel relation with the anchorage structure 5 and engages theenlarged portion of the segmental plug 11 which initially seals this endof the vent tube. In addition a sleeve 19 is initially tted around thetendon 3 within the anchorage structure 5 and may extend beyond theanchorage structure. Its inner end may be initially covered with thewrapping 4 which normally encases the tendon 3.

The construction shown in FIGURES 5 and 6 is utilized in the manner ofthe rst described structure.

After the concrete has set and the form 2 removed, the sleeve 19 isextracted along with the segmental plugs 11. The gripping wedges 8 areinserted, the tend-on 3 is tensioned and secured by the gripping wedges,and a high strength, dense grout 20 or other sealing or bonding materialis forced through the spaces between the wedge segments and into theannular space cast by the sleeve 19. The length of the sleeve and theresulting bonding connection between the grout 20 and the tendon 3 maybe such as to develop the full strength of the tendom so as tosupplement the action of the wedges 8 and provide an increased safetyfactor.

.the form 2, andsurrounding the -bolt 23, is a relatively thick-walledsleeve 26 formed of rubber or other elastomer.

With this construction the gripping wedges 8 are inserted before theconcrete is poured, and the interior of the anchorage structure 21 ispreferably filled with grease or other semisolid to exclude the entranceof cement and water and to allow axial movement of the tendon.

In the construction shown in FIGURES 7 and 8 the tendon is shown as asingle strand member having a tenacious coating 27, for example, epoxyresins, lhave been found suitable for this purpose. The epoxy resin orsimilar coating is coniined to the portion of the tendon which will beengaged by the wedges 8 and permits the use of sharper serrated teethwhile serving to keep the serrated teeth from notching into the tendonand creating stress concentrations.

After the concrete has been poured and set, the form 2, bolt 23, andsleeve 26 are removed. The tendon is then tensioned and its end severed,so as to be within the cavity cast by the sleeve 26, yand the cavity isfilled with `grout 28, as shown in FIGURE 8.

In eaoh of the constructions illustrated, the anchorage member is formedof high strength spring steel, and therefore has high hoop strength.

Furthermore, in regard to the constructions shown in FIGURES l through6, the plate 9 greatly increases the hoop strength of the anchoragemember in the region subject to the wedging action of the wedges 8.

It should be noted that the plate 9 may be incorporated in theconstruction shown in FIGURES 7 and 8 as well as in the structure shownin FIGURES 1 through 6.

Excellent bond is obtained between the exterior of the anchorage,particularly the cylindrical portions, due to the fact that concreteenters the helical groove formed by `the convolutions of the wire. Byreason of the fact that the bond between the anchorage and the concreteis distributed over a relatively large area, stress concentrations areavoided.

The bond between the concrete and the cylindrical helical coil issurprisingly effective. For example, tests have indicated that such acoil only 2 inches long is sufficient to develop the strength of aone-half inch diameter tendon. Tests have indicated that the ratio oftendon diameter to cylindrical coil length should not be less than 4:1,but need not be greater than 10:1. Furthermore, because of the fact thatthe convolutions of wire are constrained in the concrete, no failure ofthe anchorage mem-ber because of column load can occur.

Reference is now directed to FIGURES 9 through 13, wherein the anchorstructure, designated 29 is forged, or otherwise formed from highstrength steel. The anchor structure includes a tapered or conicalsleeve 30 having a tapered or conical bore 31. Midway between its ends,the sleeve is provided with an integral external constraining ange orplate 32 corresponding to the plate 9 of the first described structure.

'Bhe plate 32 is preferably square and is provided with nail holes 33which receive nails 10. Initially, the sleeve 30 receives a split rubberplug 11 'as in the first described structure. The nails ihold the sleevelightly against the cylindrical portion 13 of the plug as shown in FIG-URE 11.

The side of the plate 32 facing the cylindrical portion of the plug 11is provided with gusset webs 34 extending to the sleeve 30.

The anchorage 29 shown in FIGURES 9 through 13 is installed in the samemanner as the first described anchorage. Initially the plug 11 isinserted and the anchorage is secured to the form as shown in FIGURE l1with the tendon 3 extending therethrough.

After the concrete 1 is poured, the form and plug are removed, segmentalwedge elements 8 are inserted, `and the tendon is tensioned. The excesslength of the tendon is severed, and grouting 16 is placed in the cavityformed by the plug 11.

Operation of the anchorage 29 is essentially the same as the anchorage5, except the entire axial load of the tendon is transferred to theplate 32 for distribution to the surrounding concrete. As in the firstdescribed structure, the plate 32 is located midway between the ends ofwedging segments and completely protects the concrete from radial forceswhich would place the concrete under tension.

It should be noted that the anchorage member 5 and plate 9 are formed ofmetal and therefore, as is well known, have a modulus of elasticitygreatly in excess of concrete; for example, in the case ofsteel, it isten times as great as concrete.

While particular embodiments of this invention have been shown anddescribed, it is not intended to limit the same to the exact details ofthe constructions set forth, and it embraces such changes,modifications, and equivalents of the parts and their formation andarrangement as come within the purview of the appended claims.

What is claimed is:

1. In a stressed concrete structure having stressed tendons ofessentially circular cross-section mounted in and extending between theanchorage zones at opposite ends of said concrete structure, thecombination of an anchorage means conned to at least one anchorage zoneof said concrete structure, said means comprising:

(a) wedge-receiving element formed of metal and disposed within at leastone zone of said concrete structure, said wedge-receiving element havinga conical bore of circular cross-section;

(b) a radially extending rigid metallic constraining plate surroundingsaid wedge-receiving element intermediate its ends, said plate having aring of axially directed fastening apertures for receiving fasteningmeans to secure said wedge-receiving element to a casting form for theconcrete structure;

(c) and a body of yieldable material conforming to the interior of saidwedge-receiving means and including a portion interposed between saidwedge-receiving element and said form, and a bore therethrough receivingsaid tendon;

(d) said body being removable from said concrete structure, upon removalof said casting form, to provide access to the interior of saidwedge-receiving element.

2. A structure as defined in claim 1 wherein a portion of said body ofyieldable material is of generally cylindrical shape, and larger indiameter than said wedge receiving element and bears at one of its endson the end of said element, its other end being substantially fiat andabutting said casting form.

3. A structure as defined in claim 1 wherein said bore is substantiallyconcentric to said wedge-receiving element, said bore embracing andgripping said tendon and holding the same under slight tension; saidbody of yieldable material being split longitudinally to facilitateremoval thereof.

4. An anchorage as set forth in claim 1, wherein:

said fastening means clamps and compresses said core member between saidform and said anchor and about said tendon.

S. An anchorage as defined in claim 1 including a removable sleevesurrounding said tendon and extending through said body and anchoragemeans only in said anchorage zone and being slidably removable throughsaid body to leave a grout receiving space around said tendon in saidanchorage zone.

6. In a stressed concrete structure having stressed tendons ofessentially circular cross-section mounted in and extending between theanchorage zones at the ends of said concrete structure, the combinationof an anchorage means confined to at least one anchorage zone of saidconcrete structure, said means comprising:

(a) a wedge receiving element formed of metal and disposed within atleast one zone of said concrete structure, said wedge receiving elementhaving a -conical bore of circular cross-section;

(b) and a concial wedge fitting the bore of said wedge receiving elementfor gripping said tendon;

(c) a cylindrical element rigidly connected to the smaller end of saidwedge receiving element and continuing coaxially therewith to receivesaid tendon;

(d) the length of said cylindrical element being from 4 to 10 times thediameter of said tendon and including a series of axially spacedexternal interlocking elements directly bonded to the surroundingconcrete for transferring axial loads from said tendon to said concrete.

7. A tendon anchorage for concrete structures 4according to claim 6wherein:

(a) said conical wedge-receiving element and said cylindrical elementare formed of a continuous helically coiled wire.

8. In a stressed concrete structure having stressed tendons ofessentially circular cross-section mounted in and extending between theanchorage zones at the ends of said concrete structure, the combinationof an anchorage means confined to at least one anchorage zone of saidconcrete structure, said means comprising:

(a) a wedge receiving element formed of metal anc-1 disposed within atleast one zone of said concrete structure, said wedge receiving elementhaving a conical bore of circular cross-section;

(b) and a conical Wedge fitting the bore of said wedge receiving elementfor gripping said tendon;

(c) a cylindrical element rigidly connected to the smaller end of saidwedge receiving element and continuing coaxially therewith to receivesaid tendon;

(d) said cylindrical element including a series of axially spacedexternal interlocking elements directly bonded to the surroundingconcrete for transferring axial loads from said tendon to said concrete;

(e) said wedge receiving and cylindrical elements being formed of -acontinuous helically coiled Wire dimensioned to loosely receive saidstressing tendon to dene therewith an annular grunt-receiving cavity;

(f) and a vent tube extending from the axially inner end of saidgrout-receiving cavity to the exterior of said concrete structure, theaxial length of said groutreceiving cavity being suflicient, when filledwith grout, to effect transfer by the grout of the axial load of saidstressing tendon to said elements independeutly of said wedge means.

9. An anchorage for post stressed concrete structures adapted to havestressing tendons slidably mounted therein for tensioning after settingof the concrete comprising said structure, said anchorage being locatedin Van anchorage zone inwardly from, but adjacent at least one end ofsaid concrete structure, said anchorage comprising:

(a) a metallic, expansion resisting wedge receiving anchor secured inaxial load transmitting relation to said concrete structure within ananchorage zone inwardly from an end of said concrete structure anddelining a conical bore to receive a tendon;

(b) a yieldable, removable core member within and substantially fillingthe wedge receiving anchor and extending to the corresponding end ofsaid concrete structure and forming a grout-receiving cavity, to 35expose the interior of said wedge receiving anchor 8 and to affordaccess to the end of a tendon disposed therein;

(c) said portion of said body of yieldable material is of generallycylindrical shape and larger in diameter than said wedge receivingelement and bears at one of its ends on the end of said element, itsother end being substantially flat and flush with the end of saidconcrete structure;

(d) and a vent tube communicating at one end with the axially inner endof said grout-receiving cavity and having its other end abutting andclosed by said portion of said body of yieldable material, the axiallength of said grout-receiving cavity being suicient, when filled withgrout, to eiect transfer by the grout of the axial load of saidstressing tendon to said elements independently of said wedge means.

References Cited by the Examiner UNITED STATES PATENTS 1,940,545 12/1933Holmes 52-699 2,618,147 ll/l952 Freyssinet 52-223 2,637,895 5/1953Blaton 52-223 2,781,658 2/1957 Dobell 52-223 2,959,835 11/1960 Gates25-131 FOREGN PATENTS 544,574 2/ 1956 Belgium. 1,237,901 6/1960 France.

541,437 1l/l94l Great Britain.

612,3 24 ll/ 1948 Great Britain.

775,744 5/ 1951 Great Britain.

894,240 4/ 1962 Great Britain.

FRANK L. ABBOTT, Primary Examiner. J. L. RIDGILL, Assistant Examiner.

8. IN A STRESSED CONCRETE STRUCTURE HAVING STRESSED TENDONS OFESSENTIALLY CIRCULAR CROSS-SECTION MOUNTED IN AND EXTENDING BETWEEN THEANCHORAGE ZONES AT THE ENDS OF SAID CONCRETE STRUCTURE, THE COMBINATIONOF AN ANCHORAGE MEANS CONFINED TO AT LEAST ONE ANCHORAGE ZONE OF SAIDCONCRETE STRUCTURE, SAID MEANS COMPRISING: (A) A WEDGE RECEIVING ELEMENTFORMED OF METAL AND DISPOSED WITHIN AT LEAST ONE ZONE OF SAID CONCRETESTRUCTURE, SAID WEDGE RECEIVING ELEMENT HAVING A CONICAL BORE OFCIRCULAR CROSS-SECTION; (B) AND A CONICAL WEDGE FITTING THE BORE OF SAIDWEDGE RECEIVING ELEMENT FOR GRIPPING SAID TENDON; (C) A CYLINDRICALELEMENT RIGIDLY CONNECTED TO THE SMALLER END OF SAID WEDGE RECEIVINGELEMENT AND CONTINUING COAXIALLY THEREWITH TO RECEIVE SAID TENDON; (D)SAID CYLINDRICAL ELEMENT INCLUDING A SERIES OF AXIALLY SPACED EXTERNALINTERLOCKING ELEMENTS DIRECTLY BONDED TO THE SURROUNDING CONCRETE FORTRANSFERRING AXIAL LOADS FROM SAID TENDON TO SID CONCRETE;